Vacuum-tight insulated lead-in structure



Patented Jan. 17, 1939 UNITED STATES PATENT OFFICE VACUUM-TIGHTINSULATED LEAD-IN STRUCTUREl Pennsylvania Original application October21, 1936, Serial No. 106,798. Divided and this application February 20,1937, Serial No. 126,881

3 Claims.

My invention relates to a vacuum-tight insulated lead-in constructionand especially ysuch construction applied to electron discharge devices.

This application is a divisional application of my copendingapplication, Serial No. 106,798, iled October 21, 1936, for Vacuum-tightinsulated lead-in structures.

An object of my invention is to provide a very strong vacuum-tightlead-in construction Athat will withstand a great difference of pressureon opposite sides thereof.

Another object of my invention is to provide a construction that willpermit a plurality of insulated lead-ins through an opening in avacuumtight metal casing.

Other objects and advantages of my invention will become apparent fromthe following description and the drawing, in which:

The single figure is a View, principally in crosssection, of a dischargedevice incorporating my invention.

In the prior art devices employing seals between lead-ins and metalcontainers, glass has been heretofore utilized. In such constructions,principally that of vacuum electron discharge tubes, it is necessarythat the device be heat treated at a very high temperature in order todegasify the interior elements. An extensive portion of a glass Wallcannot be utilized with such heat treatment because the glass willbecome molten and collapse. On the other hand, if not much glass isused, there is apt to be a very short distance between the lead-in andthe metal wall of the container that will provide a leakage path withthe accumulation of dirt and moisture.

It is an object of my invention to utilize a ceramic material for thebody of insulating material and to utilize a coating of glass to sealthe ceramic material to the metal casing.

In particular, I desire to provide a Vacuumtight lead-in constructionwherein a plurality of lead-ins may extend through an opening in a metalcasing, but insulated from one another, and yet form a strong structurethat will withstand a considerable difference of pressure on theexterior and interior thereof.

In the figure, I have illustrated a casing I having a cover portion II.In this specific embodiment, the casing III contains a body of mercuryI2 which forms the cathode of this particular discharge device. Thecasing I0 has an opening I3 and about this opening is a tubularextension I4. While I have illustrated the casing II), cover II andtubular extension I4 as separate (Cl. Z50-27.5)

parts, which are welded together in vacuumtight arrangement, yet theseparts may be integral with each other or parts thereof, if desired.

I prefer to make the casing parts I0 and I I of steel or iron, and tomake the tubular extension Ill of an alloy 24% to 30% nickel, 5% to 25%cobalt, less than 1% manganese, and the remainder principally oressentially iron.

The tubular extension I4 is preferably an outwardly extending flange I5with a preferably conical out flare. Seated on this conical extension I5is an insulator I6, preferably of hollow porcelain. The adjacent face Ilof this insulator is sealed to the conical extension I5 by a coating ofglass I8. This glass is preferably of the borosilicate type having amajor percentage of silicon dioxide in a preferred range of 65% to 75%.This glass has preferably less than PbO, less than 6% A1203, and 10% to25% B203. The particular type of glass that I prefer to use has thefollowing analysis:

Percent S102 67 .3 B203 24.6 A1203 1 .7 3 N320 4.6 KzO .94 A5203 .14:I

The upper surface of the porcelain member I6 preferably has a conicalcontour I9 that is in turn sealed by glass or glaze to the under surface2i of a metal member 22 having a downwardly extending flange 23 similarin contour at its outer end to the conical contour I9 of this layer. Themetal member 22 about this central opening 24 preferably has adownwardly extending flange 25, preferably in conical shape. Seated onthis flange 25 is a second insulator 2B having a conical contour 21sealed to the flange 25 by means of glass previously described. Theinsulator 26 preferably has a central opening 28 and a lead-in conductor29 extending therethrough to the interior of the metal casing I0. Asecond metal member 30 preferably extends over the top of the insulator26 and is sealed to the top thereof at 3| by the glass previouslydescribed, The lead-in conductor 29 is, of course, preferably welded tothe under surface of the metal member 30. An exterior connection 32 maybe welded to the exterior portion of the metal member 30 and anotherlead or connection 33 welded to the other metal member 22.

I prefer to secure, by welding, a tubular lead-in to the under side ofthe metal closure member 22 extending through to the interior of themetal casing. The tubular lead-in 34 is preferably concentric with Vthecentrally disposed conductor 29. The exposed surfaces 35 and 36 of thetwo porcelain insulators may likewise be covered with a glass or glaze,as previously described.

Where this construction is used for a discharge device, I prefer tosurround the central lead-in conductor 29 with an insulating sleeve 31and to also surround the tubular lead-in 34 with another sleeve 38.'Ihese insulating sleeves are preferably of quartz.

In the particular device described, I prefer to attach an auxiliary origniting electrode 39 to the lower end of the central conductor 29. Thisigniting electrode is preferably of the make-alive type having a contactof high resistance material with the mercury pool.

The other lead-in 34 is preferably connected to an anode 4Usurroundingthe central lead-in and preferably concentric thereto. This anode ispreferably supported by a screw-threaded joint 4| to the tubular lead-in34. l

Where the glass is used for sealing purposes, I prefer to utilize theboro-silicate type of glass previously described, and where metal issealed by means of the glass, I prefer to use the nickelcobalt-ironalloy also previously described, because these substances have a similarcceiiicient of expansion substantially in the region of 4.6 to 7.0x 10-6centimeters per degree centigrade. I also' desire to utilize ceramicmaterial such as porcelain of a substantially similar coemcient ofexpansion for the insulators. One such type of porcelain is composed of30% feldspar, 25% flint and 40% clay. A typical analysis of a particulartype of this porcelain known as Derry plastic body gives:

Per cent 'SiOz 70.07 A1203 23.15 Fe203 0.39 TiOz 0.76 CaO 0.12 MgO 0.14NazO 1.09 KZO` 3.30

The specic composition of the porcelain may be varied, as for instance Ihave substituted pyrophyllite for the flint in the procelain previouslydescribed.

Although I haveshown and describedr the invention applied to a dischargetube of a particular type, many other applications of my invention arepossible to other types of discharge tubes and to other applications.Such other applications include bushing or lead-ins for condensers,especially where such bushings must be oil or air-tight, electricallead-ins for hermetically sealed refrigerators, lead-in bushings forsealed oil-filled transformers, lead-ins for motors having a specialcooling atmosphere as hydrogen, etc. 'I'his list is to be taken` asillustrative and not as a limiting list.

Also, although I have described a specific modification of my invention,various changes mayy be made in the shape, arrangement, selection andapplication of the various elements and combination disclosed. I,accordingly, desire only such limitations to be placed on the followingclaims as is necessitated by the prior art.

I claim as my invention:

l. An electrical lead-in construction comprising a metal casing portionhaving an opening, a hollow insulator sealed at one end to the casingabout said opening, a metallic member sealed to the other end of saidhollow insulator and having an opening in alingment with the hollow ofthe insulator, said metallic member having a flared portion about saidopening, a second hollow insulator having a portion corresponding incontour with said flared portion, sealing means sealing said`corresponding portions together vacuum-tight and conductor structuresealed to and extending through said second hollow insulator.

2. An electrical lead-in construction. comprising a metallic casingportion having an opening, a hollow insulator sealed at one end to thecasing about said opening, a metallic member sealed to the other end ofsaid hollow insulator and having a portion projecting within said hollowinsulator, a second hollow insulator having a portion projectingwithin'said first hollow insulator, said last mentioned projectingportions being sealed to each other and conductor structure sealed toand extending through said second hollow insulator. Y

3. An electrical lead-in vconstruction comprising a metallic casingportion having a projection about an opening, said projection having aflared end portion, a hollow insulator sealed at one end to said flaredend portion,` a metallic member having a flared edge portion sealed tothe other end of said hollow insulator and having an opening with a arededge, a second hollow insulator having one end sealed to said lastmentioned flared edge and conductor structure sealed to the other end ofsaid second insulator.

WALTER E. BA1-ILS.

